The invention relates to a device for collecting printed sheets into non-bound book blocks along a horizontal feed section, including a conveying arrangement with a circulating traction device. The device also includes successively mounted and spaced apart conveying elements for accommodating the printed sheets. The printed sheets are arranged on the circulating traction device. Above-positioned feed devices for the printed sheets are also provided which are mounted successively in the conveying direction along the traction device. The conveying elements, which are guided in at least one feed region for the printed sheets, are embodied as support surfaces for the collected, stacked sheets. The support surfaces have an end stop at the front end in the circulating or conveying direction and the end stop extends transverse to the conveying direction.
Collecting devices of the aforementioned type are used in industrial bookbinding operations for collecting printed sheets into loose stacks (book blocks). In the process, the various printed sheets are collected in a predetermined sequence and are then transferred to a different machine for the further processing, for example to a perfect binder, where they are bound to form unfinished books, catalogs, brochures, or similar printed products. The collecting devices disclosed in some references are provided with a conveying arrangement consisting of a circulating traction device with uniformly spaced-apart conveying elements mounted thereon. Feed devices are positioned along the conveying arrangement, which generally feed respectively one printed sheet to the conveying elements of the conveying arrangement during each operating cycle. The conveying elements are essentially embodied as supports onto which the printed sheets are deposited with their flat sides down or on which they are stacked and are provided with an end stop positioned perpendicular to the support surface, which is designed for aligning the sheets. A defined type of printed sheets is stored in each feed device, of which respectively one is supplied to the conveying elements passing by, so that when reaching the end of the conveying arrangement the conveying elements carry loose book blocks composed of individual sheets.
European patent document 1 726 552 A1 discloses an apparatus, designed to be used for processing printed sheets, which is provided with conveying elements having a wall at the front end in conveying direction and support surfaces that are slanted toward this wall, at least in the region of the conveying or feed section. The angle β formed by the conveying direction L and the slanted support surface is smaller than the feed angle α between the conveying direction L and the feed direction F of the feed devices. This type of arrangement is based on the idea of positioning the printed sheets, which are supplied by the feed devices from above and at an angle in a downward direction, in approximately the same slanted position on the support surfaces of the conveying elements.
Tests carried out with this type of arrangement have shown, however, that positioning the surfaces of the conveying elements at a slant does not work if the weight of the individual printed sheets to be collected differs considerably. For example, if a more light-weight sheet is supplied to the support surface and a relatively heavy printed sheet is then pushed on top of this sheet, the heavier sheet pushed on top can displace the sheet underneath in the region along the end stop because of the frictional engagement.
This problem cannot be corrected, not even with an embodiment as disclosed in International Patent Application Publication No. WO 2007/085101 A1, which stipulates that the support surfaces of the conveying elements driven along a circular path must be embodied to be at an angle in the conveying direction, at least in the feed region for the printed sheets, or must be placed at an angle. However, it is possible that the slanted position of the conveying element support surfaces may help the movement of the printed sheets into the conveying elements.
European patent document 1 726 552 A1 and International Patent Application Publication No. WO 2007/085101 A1 obviously proceed on the assumption that the feeding, collecting, and aligning of the printed sheets on the support surfaces of the conveying elements can be aided by positioning these at an angle. This opinion is incorrect because experience has shown that the printed sheets cannot be reliably aligned and collected on the slanted support surfaces of the conveying elements, such that they rest thereon.